Liverpool will sack Jurgen Klopp if they fail to qualify for the Champions League or win a trophy this season.
Klopp was appointed manager in October 2015, replacing the sacked Brendan Rodgers and taking the club to two finals in his first campaign
Liverpool were beaten in both the Capital One Cup and Europa League finals that season, and remain without silverware under Klopp.
The German took the Reds to Champions League qualification for the first time since the 2014/15 season and they are currently on course to reach the knock-out stages.
But speaking on the Transfer Window podcast, Castles predicted that failure to win a trophy or qualify for the Champions League would bring about Klopp’s demise.
“Liverpool will twist if Klopp fails to get Champions League football or win a trophy this season – which is looking a distinct possibility.
“If I was Liverpool, I would try to hire Marco Silva as his replacement.”